TECHNICAL FIELD
[0001] The present invention relates to a polysilane production process.
BACKGROUND ART
[0002] The formation of a silicon thin film (such as an amorphous silicon film or a polysilicon
film) pattern for use in integrated circuits and thin film transistors is generally
carried out by removing unrequired portions by photolithography after a silicon film
is formed on the entire surface by a vacuum process such as CVD (Chemical Vapor Deposition).
However, this process involves the following problems: large-scale equipment is required,
the use efficiency of raw materials is low, it is difficult to handle the raw materials
because they are gaseous, and a large amount of waste is produced. Therefore, a process
(coating process) for forming a silicon film by applying a polysilane having a high
molecular weight to a substrate and heating or exposing it to UV has recently been
proposed.
[0003] However, in the method of directly synthesizing a silane compound having a high molecular
weight, the synthesizing procedure and the purification method are generally extremely
difficult.
JP-A 11-260729 discloses a method of directly synthesizing a high-order silane by thermopolymerization.
However, in this technology, Si
9H
20 is merely obtained at a low yield and the size of this molecule is still unsatisfactory
for the development of performance such as wettability required for the application
of this molecule in the coating process.
[0004] Meanwhile, a method of obtaining a high-order silane compound by applying ultraviolet
radiation to a solution of a silane compound having photopolymerizability so as to
photopolymerize it has been disclosed (
JP-A 2003-313299). However, this technology has a problem that large-scale equipment is required for
a photopolymerization reaction.
DISCLOSURE OF THE INVENTION
[0005] It is therefore an object of the present invention to provide a polysilane production
process which eliminates the need for large-scale equipment and can be carried out
under mild conditions.
[0006] The inventors of the present invention have conducted intensive studies to attain
the above object and have found that a specific metal complex catalyst has such high
activity in the polymerization reaction of a silane compound that a polysilane is
obtained even under mild reaction conditions such as room temperature and 1 atm. The
present invention has been accomplished based on this finding.
[0007] That is, according to the present invention, the above object and advantage of the
present invention are attained by a polysilane production process comprising reacting
at least one silane compound selected from the group consisting of a linear silane
compound represented by the following formula (1), a cyclic silane compound represented
by the following formula (2) and a cage-shaped silane compound represented by the
following formula (3) in the presence of a binuclear metal complex represented by
the following formula (4).
Si
iH
2i+2 (1)
(in the formula (1), i is an integer of 1 to 8.)
Si
jH
2j (2)
(in the formula (2), j is an integer of 3 to 10.)
Si
kH
k (3)
(in the formula (3), k is 6, 8 or 10.)
[CpM(µ-CH
2)]
2 (4)
(in the formula (4), Cp is a cyclopentadienyl-based ligand, M is a metal atom selected
from Rh and Ir, and the bond between M's is a double bond.)
Brief Description of the Drawings
[0008]
Fig. 1 is an IR spectral chart of a polysilane obtained in Example 1;
Fig. 2 is a GPC spectral chart of the polysilane obtained in Example 1; and
Fig. 3 is a 1H-NMR spectral chart of the polysilane obtained in Example 1.
Mode for Carrying Out the Invention
[0009] The polysilane production process of the present invention will be described in detail
hereinunder.
[0010] The silane compound used in the process of the present invention is at least one
selected from the group consisting of a linear silane compound represented by the
above formula (1), a cyclic silane compound represented by the above formula (2) and
a cage-shaped silane compound represented by the above formula (3).
[0011] The silane compound used in the process of the present invention is preferably at
least one selected from the group consisting of a linear silane compound represented
by the above formula (1) and a cyclic silane compound represented by the above formula
(2). The linear silane compound represented by the above formula (1) is particularly
preferably at least one selected from the group consisting of SiH
4 (monosilane), Si
2H
6 (disilane) and Si
3H
8 (trisilane). The cyclic silane compound represented by the above formula (2) is particularly
preferably at least one selected from the group consisting of cyclopentasilane represented
by the following formula (2-A), cyclohexasilane represented by the following formula
(2-B) and silylcyclopentasilane represented by the following formula (2-C).

[0012] The silane compound in the present invention is preferably a cyclic silane compound
represented by the above formula (2), particularly preferably at least one selected
from the group consisting of the compounds represented by the above formulas (2-A),
(2-B) and (2-C).
[0013] These preferred silane compounds can be produced through decaphenylcyclopentasilane
and dodecaphenylcyclopentasilane produced from diphenyldichlorosilane. These silane
compounds may be used alone or in combination of two or more.
[0014] The binuclear metal complex used in the process of the present invention is a complex
represented by the above formula (4). This complex has high activity and is particularly
effective in the polysilane production process of the present invention. The reason
for this is assumed to be that the electron density between metal atoms is high due
to the double bond between M's with the result of strong reducing power.
[0015] The cyclopentadienyl-based ligand in the above nuclear metal complex is, for example,
a cyclopentadienyl ligand or substituted cyclopentadienyl ligand represented by the
following formula (5).

(in the formula (5), R
1, R
2, R
3, R
4 and R
5 are each independently a hydrogen atom, alkyl group having 1 to 5 carbon atoms, aryl
group having 6 to 14 carbon atoms, trifluoromethyl group or trialkylsilyl group having
an alkyl group with 1 to 4 carbon atoms.)
[0016] Examples of the aryl group having 6 to 14 carbon atoms include phenyl group, naphthalenyl
group and anthracenyl group.
[0017] The cyclopentadienyl-based ligand is preferably an alkyl-substituted cyclopentadienyl
ligand of the above formula (5) in which 1 to 5 out of R
1, R
2, R
3, R
4 and R
5 are alkyl groups having 1 to 5 carbon atoms and the rest are hydrogen atoms; an aryl-substituted
cyclopentadienyl ligand of the above formula (5) in which 1 to 5 out of R
1, R
2, R
3, R
4 and R
5 are aryl groups having 6 to 14 carbon atoms and the rest are hydrogen atoms; or a
trialkylsilyl-substituted cyclopentadienyl ligand of the above formula (5) in which
1 to 5 out of R
1, R
2, R
3, R
4 and R
5 are trialkylsilyl groups having an alkyl group with 1 to 4 carbon atoms and the rest
are hydrogen atoms.
[0019] The cyclopentadienyl-based ligand is particularly preferably a pentamethylcyclopentadienyl
ligand (η
5-C
5(CH
3)
5, to be also referred to as "Cp*" hereinafter) which is easily acquired and has high
electron releasability from the viewpoints of further increasing the electron density
chemically and maintaining the three-dimensional shape stability of a reaction field.
Therefore, the binuclear metal complex used in the process of the present invention
is particularly preferably a complex represented by the above formula (6) or (9).
[0020] To synthesize the above binuclear metal complex [CpM(µ-CH
2)]
2, for example, [CpM(µ-CH
2)CH
3]
2 is reacted with hydrogen chloride to obtain [CpM(µ-CH
2)Cl]
2 which is then reacted with Na.
[0021] The synthesis of the starting material [CpM(µ-CH
2)CH
3]
2 may be carried out in accordance with the method described in
J. Chem. Soc., Dalton Trans., 1441-1447 (1983). The reaction between [CpM(µ-CH
2)Cl]
2 and hydrogen chloride may be carried out in accordance with the method described
in
J. Chem. Soc., Dalton Trans., 1215-1221 (1984). Stated more specifically, the temperature of a solution containing [CpM(µ-CH
2)CH
3]
2 is adjusted to 0 to 30°C, and hydrogen chloride is blown into the solution to carry
out the reaction. As a solvent for this reaction may be used pentane, toluene, dichloromethane
or chloroform. Then, Na is added to the obtained solution containing [CpM(µ-CH
2)Cl]
2 to carry out a reaction, a precipitate is removed, and a powder obtained by removing
the solvent is purified by a suitable technique such as recrystallization to obtain
the binuclear metal complex [CpM(µ-CH
2)]
2 of interest. As the solvent contained in the solution containing [CpM(µ-CH
2)Cl]
2 may be used benzene, toluene, hexane, pentene, cyclohexane or tetrahydrofuran.
[0022] In the process of the present invention, the above silane compound is reacted in
the presence of the above binuclear metal complex. This reaction is preferably carried
out in a liquid state. When the starting material silane compound is liquid, it may
be mixed with the binuclear metal complex in the absence of a solvent but the above
reaction is preferably carried out in the presence of a suitable solvent. The solvent
which can be used herein is not particularly limited as long as it dissolves the silane
compound and does not react with the compound and the above binuclear metal complex.
Examples of the solvent include hydrocarbon solvents such as n-pentane, n-hexane,
n-heptane, n-octane, n-decane, dicyclopentane, benzene, toluene, xylene, durene, indene,
tetrahydronaphthalene, decahydronaphthalene and squalane; ether solvents such as dipropyl
ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol
methyl ethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether,
diethylene glycol methyl ethyl ether, tetrahydrofuran, tetrahydropyran and p-dioxane;
and polar solvents such as propylene carbonate, γ-butyrolactone, N-methyl-2-pyrrolidone,
dimethyl formamide, acetonitrile and dimethyl sulfoxide. Out of these, hydrocarbon
solvents and ether solvents are preferred, and hydrocarbon solvents are particularly
preferred from the viewpoints of the solubility of the silane compound and the stability
of the solution. These solvents may be used alone or in combination of two or more.
[0023] The amount of the solvent is such that the concentration of the silane compound in
the obtained solution becomes preferably not less than 0.1 mass%, more preferably
0.5 to 10 mass%.
[0024] The amount of the binuclear metal complex is preferably 5 x 10
-4 to 5 x 10
-1 mol, more preferably 1 x 10
-3 to 1 x 10
-1 mol based on 1 mol of the silane compound as the starting material. When the amount
of the binuclear metal complex is smaller than 5 x 10
-4 mol, the reaction may not proceed sufficiently and when the amount is larger than
5 x 10
-1 mol, the molecular weight of the obtained polysilane may become too low.
[0025] The temperature for the reaction of the silane compound in the presence of the binuclear
metal complex is preferably -30 to 100°C, more preferably 0 to 50°C. The pressure
for the reaction is preferably 1 x 10
4 to 1 x 10
6 N/m
2, more preferably 5 x 10
4 to 2 x 10
5 N/m
2, particularly preferably 1 atm. (1.01 x 10
4 N/m
2). The reaction time is preferably 10 minutes to 50 hours, more preferably 1 to 30
hours.
[0026] The weight average molecular weight of the polysilane obtained as described above
can be adjusted to any value according to its use purpose and use manner by suitably
setting the amount of the binuclear metal complex, the reaction temperature, the reaction
pressure and the reaction time. The weight average molecular weight of the polysilane
obtained by the process of the present invention can be set to, for example, 500 to
500,000, specifically 2,000 to 100,000. The weight average molecular weight is a value
in terms of polystyrene measured by gel permeation chromatography (GPC).
[0027] It is preferred that the binuclear metal complex should be removed from the polysilane
solution obtained by the process of the present invention. The removal of the binuclear
metal complex from the polysilane solution can be carried out by the following methods:
(1) the polysilane solution is let flow into a suitable column containing silica gel
or alumina to adsorb the binuclear metal complex, (2) the polysilane solution is washed
in deaerated water, and (3) a poor solvent for the binuclear metal complex is added
to the polysilane solution to precipitate the binuclear metal complex and the obtained
precipitate is removed by filtration.
[0028] The polysilane solution obtained by the process of the present invention can be advantageously
used as a composition for forming a silicon film which is used in integrated circuits,
thin film transistors, photoelectric converters and photoreceptors.
[0029] The polysilane solution obtained by the process of the present invention can be used
as a composition containing other additives as required. For example, a desired n-type
or p-type silicon film containing a dopant can be formed by adding a substance containing
the group 3B element or the group 5B element of the periodic table as a dopant source
to the polysilane solution. The wettability of an object to be coated by the solution
can be further improved, the leveling properties of the coating film can be improved
and the production of irregularities on the coating film and an orange-peel skin can
be prevented by adding a small amount of a fluorine-based, silicone-based or nonionic
surfactant to the polysilane solution as required.
Examples
[0030] The following examples are provided for the purpose of further illustrating the present
invention but are in no way to be taken as limiting.
Synthesis Example 1 (synthesis of binuclear rhodium complex)
[0031] [Cp*Rh(µ-CH
2)Cl]
2 was first synthesized in accordance with the method described in
J. Chem. Soc., Dalton Trans., 1215-1221 (1984). Stated more specifically, when the temperature of a pentane solution of [Cp*Rh(µ-CH
2)Me]
2 was adjusted to 20°C and a hydrogen chloride gas was blown into this solution to
carry out a reaction at the same temperature for 3 minutes, the color of the solution
became dark purple, and a reddish brown precipitate was obtained. The obtained precipitate
was collected and purified by recrystallization to obtain [Cp*Rh(µ-CH
2)Cl]
2.
[0032] Then, 203 mg (0.353 mmol) of the obtained [Cp*Rh(µ-CH
2)Cl]
2 was dissolved in 20 mL of anhydrous benzene, and 64 mg of Na was added to this. When
this solution was stirred for 5 hours, a white precipitate separated out, and the
color of the solution changed from red to turquoise. After the precipitate was removed
by filtration, the solvent was removed from the obtained solution to obtain a dark-blue
powder (yield of 168 mg, yield rate of 95 % (based on Rh)). The reaction formula of
this reaction is as follows.
[Cp*Rh(µ-CH
2)Cl]
2 + 2Na → [Cp*Rh(µ-CH
2)]
2 + 2NaCl
[0033] The obtained dark-blue powder was recrystallized with toluene to obtain a blue crystal.
When
1H-NMR,
13C-NMR and UV spectra (UV/vis) of this crystal were measured, it was found that this
crystal was a complex represented by the above formula (6). The results of
1H-NMR and UV spectra are given below.
1H-NMR (400 MHz, C
6D
6) : δ1.64 (s, C
5Me
5, 30H), 9.44 (t, µ-CH
2, 4H)
13C-NMR (100 MHz, C
6D
6) : δ157.2, 93.5, 10.8
UV/vis (C
6H
6) : λmax = 606 nm (ε = 1.02 x 10
4 M
-1 cm
-1)
Synthesis Example 2 (synthesis of binuclear iridium complex)
[0034] The starting material [Cp*Ir(µ-CH
2)Cl]
2 was first synthesized in the same manner as in the above Synthesis Example 1.
[0035] Then, [Cp*Ir(µ-CH
2)Cl]
2 (203 mg, 0.269 mmol) was dissolved in anhydrous benzene (20 mL) in a nitrogen atmosphere,
and Na (64 mg) was added to the resulting solution. When this solution was stirred
for 5 hours, a white precipitate separated out and the color of the solution changed
from reddish orange to purple. After the precipitate was removed by filtration, the
solvent was removed from the obtained solution to obtain a red powder (yield of 181
mg, yield rate of 98 % (based on Ir)). The reaction formula is as follows.
[Cp*Ir(µ-CH
2)Cl]
2 + 2Na → [Cp*Ir(µ-CH
2)]
2 +2NaCl
[0036] The obtained red powder was recrystallized with tetrahydrofuran to obtain a red crystal.
It was found from the NMR and UV spectra that the obtained red crystal was a binuclear
metal complex represented by the above formula (9).
1H-NMR (400 MHz, C
6D
6) : δ1.72 (s, C
5Me
5, 30H), 9.01 (s, µ-CH
2, 4H)
13C-NMR (100 MHz, C
6D
6) : δ88.7, 88.1, 10.6
UV/vis(C
6H
6) : λmax = 474 nm (ε = 1.43 x 10
4 M
-1 cm
-1)
Synthesis Example 3 (synthesis of binuclear rhodium complex)
[0037] The starting material [Cp(SiMe
3)
5Rh(µ-CH
2)Cl]
2 was first synthesized in the same manner as in the above Synthesis Example 1.
[0038] Then, [Cp(SiMe
3)
5Rh(µ-CH
2)Cl]
2 (266 mg, 0.350 mmol) was dissolved in anhydrous benzene (20 mL) in a nitrogen atmosphere,
and Na (64 mg) was added to the resulting solution. When this solution was stirred
for 5 hours, a white precipitate separated out. After the precipitate was removed
by filtration, the solvent was removed from the obtained solution to obtain a powder
(yield of 222 mg, yield rate of 92 % (based on Rh)). The reaction formula is as follows.
[Cp(SiMe
3)
5Rh(µ-CH
2)Cl]
2 + 2Na → [Cp(SiMe
3) 5Rh (µ-CH
2)]
2 +2NaCl
[0039] It was found from the NMR and UV spectra that the obtained powder was a binuclear
metal complex represented by the above formula (7).
Synthesis Example 4 (synthesis of binuclear rhodium complex)
[0040] The starting material [Cp(Ph)Rh(µ-CH
2)Cl]
2 was first synthesized in the same manner as in the above Synthesis Example 1.
[0041] Then, [Cp(Ph)Rh(µ-CH
2)Cl]
2 (206 mg, 0.351 mmol) was dissolved in anhydrous benzene (20 mL) in a nitrogen atmosphere,
and Na (64 mg) was added to the resulting solution. When this solution was stirred
for 5 hours, a white precipitate separated out. After the precipitate was removed
by filtration, the solvent was removed from the obtained solution to obtain a powder
(yield of 170 mg, yield rate of 94 % (based on Rh)). The reaction formula is as follows.
[Cp(Ph)Rh(µ-CH
2)Cl]
2 + 2Na → [Cp(Ph)Rh(µ-CH
2)]
2 + 2NaCl
[0042] It was found from the NMR and UV spectra that the obtained powder was a binuclear
metal complex represented by the above formula (8).
Example 1 (Synthesis Example 1 of polysilane)
[0043] 0.3875 g (2.5 mmol) of cyclopentasilane was dissolved in 10 g of deaerated toluene
to obtain a cyclopentasilane solution. When 12.55 mg (0.025 mmol) of the binuclear
rhodium complex represented by the above formula (6) obtained in the above Synthesis
Example 1 was added to the obtained cyclopentasilane solution and stirred at 25°C
and 1 atm. for 24 hours, a reddish brown viscous solution was obtained. Then, the
obtained viscous solution was applied to a silica gel column (Kieselgel 60 of Merck
& Co., Inc.) to be purified so as to remove the binuclear rhodium complex. When infrared
spectroscopy analysis, GPC analysis and
1H-NMR analysis were made on the colorless transparent viscous solution obtained after
column purification, it was found that this solution was a solution containing a polysilane.
<infrared spectroscopy analysis>
[0044] After the obtained viscous solution was applied to a KBr plate in a nitrogen atmosphere
and the solvent was removed from the solution, the IR absorption spectrum of the obtained
product was measured in a glove box in a nitrogen atmosphere at 25°C. The measured
IR spectral chart is shown in Fig. 1.
IR (neat): 2, 108 cm
-1 (ν
Si-H), 893 cm
-1, 847 cm
-1 (ν
Si-H)
<GPC analysis>
[0045] The solvent was removed from the obtained viscous solution and the resulting solution
was dissolved in cyclohexane to prepare a 1 mass% cyclohexane solution. When GPC analysis
was made on the prepared cyclohexane solution under the following conditions, it was
found that the obtained polysilane had a weight average molecular weight (Mw) of 9,500
and a molecular weight distribution index (Mw/Mn) of 1.45. The measured GPC spectral
chart is shown in Fig. 2.
[measurement instrument]
[0046] The GPCMAX and TDA-302 of VISCOTEK were brought into the glove box as a gel permeation
chromatograph analyzer to carry out GPC analysis in a nitrogen gas stream at an oxygen
concentration of 10 ppm or less.
[column for gel permeation chromatography]
[0047] The TSK-GELG3000HHR, TSK-GELG2000HHR and TSK-GELG1000HHR (these columns containing
a styrene-divinylbenzene copolymer having a particle diameter of 5 µm) of Tosoh Corporation
were connected in series as columns for GPC analysis.
[solvent]
[0048] Cyclohexane (manufactured by Wako Pure Chemical Industries, Ltd.) was used as a solvent
for GPC analysis.
[standard sample]
[0049] Polystyrene (TSK standard POLYSTYRENE of Tosoh Corporation) was used.
<1H-NMR analysis>
[0050] The solvent was removed from the obtained viscous solution and the resulting solution
was dissolved in benzene-d
6 to carry out 300 MHz
1H-NMR analysis on the solution with tetramethylsilane as an internal standard. The
measured
1H-NMR spectral chart is shown in Fig. 3.
1H-NMR (300 MHz, C
6D
6) : δ3.24 (3.0 - 4.0 ppm)
Example 2 (Synthesis Example 2 of polysilane)
[0051] A reaction was carried out under the same conditions as in the above Example 1 except
that 16.4 mg (0.025 mmol) of the binuclear iridium complex represented by the above
formula (9) obtained in the above Synthesis Example 2 was used in place of the binuclear
rhodium complex in Example 1 to obtain a colorless transparent viscous solution.
[0052] When
1H-NMR analysis, infrared spectroscopy analysis and GPC analysis were made on this
viscous solution in the same manner as in Example 1, it was found that this was a
solution containing a polysilane having a weight average molecular weight of 5,500.
Example 3 (Synthesis Example 3 of polysilane)
[0053] When 0.45 g (2.5 mmol) of silylcyclopentasilane was dissolved in 10 g of deaerated
toluene and 13 mg (0.025 mmol) of the binuclear rhodium complex represented by the
above formula (6) obtained in Synthesis Example 1 was added to the resulting solution
and stirred at 25°C and 1 atm. for 2 hours, a reddish brown viscous solution was obtained,
accompanied by the production of a violent hydrogen gas. This viscous solution was
applied to a silica gel column (Kieselgel 60 of Merck & Co., Inc.) to be purified
so as to remove the binuclear rhodium complex, thereby obtaining a colorless transparent
viscous solution.
[0054] When
1H-NMR analysis and infrared spectroscopy analysis were made on this viscous solution
in the same manner as in Example 1, it was found that this viscous solution was a
solution containing a polysilane. It was also found by GPC measurement that this polysilane
had a weight average molecular weight (Mw) of 12,000 and a number average molecular
weight (Mn) of 4,000.
[0055] The silylcyclopentasilane used in this Example was synthesized in accordance with
the method described in
JP-A 2001-253706 (same as in Example 4).
Example 4 (Synthesis Example 4 of polysilane)
[0056] 0.45 g (2.5 mmol) of silylcyclopentasilane was dissolved in 10 g of deaerated tetralin,
and 27 mg (0.025 mmol) of the binuclear rhodium complex represented by the above formula
(7) obtained in the above Synthesis Example 3 was added to the resulting solution
and stirred at 40°C and 1 atm. for 24 hours. Right after the addition of the complex,
a hydrogen gas was produced and a reddish brown viscous solution was obtained in the
end. This viscous solution was applied to a silica gel column (Kieselgel 60 of Merck
& Co., Inc.) to be purified so as to remove the binuclear rhodium complex, thereby
obtaining a colorless transparent viscous solution.
[0057] When
1H-NMR analysis and infrared spectroscopy analysis were made on this viscous solution
in the same manner as in Example 1, it was found that this viscous solution was a
solution containing a polysilane. It was also found by GPC measurement that this polysilane
had a weight average molecular weight (Mw) of 1,800 and a number average molecular
weight (Mn) of 870.
Example 5 (Synthesis Example 5 of polysilane)
[0058] 0.45 g (2.5 mmol) of cyclohexasilane was dissolved in 10 mL of deaerated cyclohexane
in a glove box in a nitrogen atmosphere. 13 mg (0.025 mmol) of the binuclear rhodium
complex represented by the above formula (8) obtained in the above Synthesis Example
4 was added to this solution and stirred at 25°C and 1 atm. for 2 hours to obtain
a viscous solution. This viscous solution was applied to a silica gel column (Kieselgel
60 of Merck & Co., Inc.) to be purified so as to remove the binuclear rhodium complex,
thereby obtaining a colorless transparent viscous solution.
When
1H-NMR analysis and infrared spectroscopy analysis were made on this viscous solution
in the same manner as in Example 1, it was found that this viscous solution was a
solution containing a polysilane. It was also found by GPC measurement that this polysilane
had a weight average molecular weight (Mw) of 10,700 and a number average molecular
weight (Mn) of 4,200.
The cyclohexasilane used in this Example was synthesized by chlorinating dodecaphenylcyclohexasilane
obtained by the Kipping reaction of diphenyldichlorosilane with hydrogen chloride
in the presence of an aluminum chloride catalyst and reducing the chlorinated product
with hydrogenated lithium aluminum.
Effect of the Invention
[0059] According to the present invention, there is provided a polysilane production process
which eliminates the need for large-scale equipment and can be carried out under mild
conditions such as room temperature and 1 atm.